Multicolour sketch recognition in a learning environment.

Virtual physics environments are becoming increasingly popular as a teaching tool for grade and high school level mechanical physics. While useful, these tools often offer a complex user interface, lacking the intuitive nature of the traditional whiteboard. Furthermore, the systems are often too advanced to be used by novices for further experimentation. In this paper we describe a physics learning environment using multicolour sketch recognition techniques on digital whiteboards. We argue that the use of coloured pens helps to resolve several ambiguities appearing in single colour sketching interfaces. The recognition system is based on a combination of Support Vector Machines and rule based methods. The system was evaluated using a constructive interaction method, with users completing a set task

Trivalent expanders and hyperbolic surfaces

We introduce a family of trivalent expanders which tessellate compact hyperbolic surfaces with large isometry groups. We compare this family with Platonic graphs and modifications of them and prove topological and spectral properties of these families

Mesh alignment using grid based PCA.

We present an algorithm for mesh alignment by performing Principal Components Analysis (PCA) on a set of nodes of a regular 3D grid. The use of a 3D lattice external to both inputs increases the robustness of PCA, particularly when dealing with meshes of different and possibly uneven vertex density. The proposed algorithm was tested on meshes that have undergone standard mesh processing operations such as smoothing, simplification and remeshing. In several cases the results indicate an improved robustness compared to performing PCA directly on mesh vertices

Evaluating the Resilience of Face Recognition Systems Against Malicious Attacks

This paper presents an experiment designed to test the resilience of several user verification systems based on face recognition technology against simple identity spoofing methods, such as trying to gain access to the system by using mobile camera shots of the users, their ID cards, or social media photos of them that are available online. We also aim at identifying the compression threshold above which a photo can be used to gain access to the system. Four major user verification tools were tested: Keyemon and Luxand Blink on Windows and Android Face Unlock and FaceLock on Android. The results show all tested systems to be vulnerable to even very crude attacks, indicating that the technology is not ready yet for adoption in applications where security rather than user convenience is the main concern

Designing a facial spoofing database for processed image attacks

Face recognition systems are used for user authentication in everyday applications such as logging into a laptop or smartphone without need to memorize a password. However, they are still vulnerable to spoofing attacks, as for example when an imposter gains access to a system by holding a printed photo of the rightful user in front of the camera. In this paper we are concerned with the design of face image databases for evaluating the performance of anti-spoofing algorithms against such attacks. We present a new database, supporting testing against an enhancement of the attack, where the imposter processes the stolen image before printing it. By testing a standard antispoofing algorithm on the new database we show a significant decrease in its performance and, as a simple remedy to this problem, we propose the inclusion of processed imposter images into the training set

Colour processing in adversarial attacks on face liveness systems.

In the context of face recognition systems, liveness test is a binary classification task aiming at distinguishing between input images that come from real people’s faces and input images that come from photos or videos of those faces, and presented to the system’s camera by an attacker. In this paper, we train the state-of-the-art, general purpose deep neural network ResNet for liveness testing, and measure the effect on its performance of adversarial attacks based on the manipulation of the saturation component of the imposter images. Our findings suggest that higher saturation values in the imposter images lead to a decrease in the network’s performance. Next, we study the relationship between the proposed adversarial attacks and corresponding direct presentation attacks. Initial results on a small dataset of processed images which are then printed on paper or displayed on an LCD or a mobile phone screen, show that higher saturation values lead to higher values in the network’s loss function, indicating that these colour manipulation techniques can indeed be converted into enhanced presentation attacks